This invention pertains to a process for the preparation of porous or cellular resinous articles.
A search was made of the patent art and no art anticipatory of the claimed invention of the present application was found. None of the processes described in the prior art involved instant foam type processes and none encountered the problem that was encountered and solved by applicants; however, the art found in the search is as follows:
U.S. Pat. No. 2,256,483 describes a process for producing synthetic spongy material, particularly from a polymer of ethylene. This process shown in the figure is carried out at elevated temperatures at which the polymer is molten, and a ribbon or sheet of spongy polymer is extruded through a die. It is stated on page 3, column 1, line 56-62, that further control of pore size in the sponge prepared by extrusion of a froth may be obtained by passing the molten froth through a screen prior to extrusion.
U.S. Pat. No. 3,232,709 describes a foam generating apparatus for generating and forming a plastic foam. In the second paragraph of the patent, it is stated that the materials, for example, may constitute a resin and a suitable prepolymer such as toluene diisocyanate which, upon contact with each other, will interact and expand to provide the desired foam. In column 4, lines 33-37, it is stated that the foam material will then continue out through the screening material 29 which aids in providing a more homogeneous consistency to the material which then passes from the outlet nozzle 28. The screen is also shown in the drawing. This screen serves to homogenously mix the reacting ingredients which form the solid form.
U.S. Pat. No. 3,286,992 is titled mixing device. The drawings show a device for mixing two fluids to form a foam. A polyurethane foam is described in column 5, lines 28-33, and screen packing of the nozzle is said to increase the uniformity of the cell size even further, with the screens being shown in FIG. 2.
U.S. Pat. No. 3,461,193 describes a novel procedure for starting the flash-extrusion of expandable resin compositions. In this patent, column 4, lines 27-33, is described a filter upstream of the orifices and the filter is ordinarily a screen-pack with mesh fine enough to prevent the passage of any particles capable of plugging the orifices but with open area very large with respect to orifice-area so as to prevent large relative pressure drops across filters.
U.S. Pat. No. 3,026,273 describes a process for making expandable vinyl aromatic resin compositions. The drawing shows a screw extruder and a screen or strainer is shown before the nozzle of the extruder, column 2, lines 33-37. The polymer is heated to melt it before extrusion as indicated in column 2, lines 57-59.
In the absence of the improvement of the present invention the instant foam process is an uncontrollable process as far as forming uniformly shaped articles. The speed of the foam through the die must be slowed down sufficiently to allow the die to shape the article. In the instant foam process a quick-opening ball value is used and a value of this nature must be used since a normal valve as a needle valve tears up the foam. In the prior art processes discussed above the screens or other restrictions are always used for mixing, filtering or controlling pore size or homogeneity of the foam, and in no case was a screen, perforated plate or other restriction used to control the shape of the foam article as in applicant's instant foam process. Also, it should be noted that a screen is not needed to control foam pore size in the instant foam process and that the shaping can be done by baffles, an elongated die, a tapered elongated die, equivalent restrictive means or combinations of these means with or without a screen.
The products of the present invention are useful for preparing energy management foams for air dropped loads, flotation devices, for packaging of delicate equipment, for emergency splints for personal injuries, for thermal insulation, for closing openings, for decorative purposes, etc. The foam is generally low-density with predominately closed-cell structure having high compressive strength and dimensional stability, with small uniform cells. Its whiteness makes it attractive for aesthetic reasons. However, it may be dyed readily, as by adding a soluble dye such as Congo Red or Brom Cresol Green in suitable concentration to the foamable mixture, e.g. 0.2-2.0% by weight of the solid foam.